1. Field of the Invention
This invention relates to friction stir welding pin-tools, and more particularly to pin design and the pin surface geometry which engages a workpiece.
2. Description of Related Art
Friction Stir Welding (FSW) is a solid-state welding process that uses a non-consumable rotating pin-tool to make linear welds. Typical pin-tools consist of a cylindrical “shoulder” and a smaller diameter protruding “pin”. The process is initiated by plunging the rotating pin-tool into a weld joint until the shoulder is in intimate contact with the surface of the work piece. After the pin-tool has reached its final plunge depth a dwell-time is initiated wherein the material surrounding the pin-tool is heated by friction and plastic deformation. Travel is initiated after sufficient dwell-time, and the weld is created by literally stirring plasticized material together under compressive forces generated by the tool shoulder. Finally, the weld is concluded by halting travel and withdrawing the rotating pin-tool from the work piece.
Friction stir welding (FSW) is a relatively new technology but because of its broad applicability in the welding industry (as a replacement for fusion welding processes) it is the focus of significant research and development. The process is still in its infancy and has already been implemented in several production applications in the aerospace, automotive, rail, and trucking industries.
Accordingly, improvements in pin-tool design are believed to be important to provide industry with quality tools so that FSW will be an attractive option for manufacturers and metal workers.
Several patent applications have been filed, and some patents granted on friction stir welding tools. U.S. Patent Application Publication No. US 2002/0011509 shows a probe for friction stir welding having a shank, a shoulder and a pin-tool. No pin sleeves are shown or described in this reference. U.S. Patent Application Publication No. US 2002/0179682 shows a method and apparatus for joining work pieces by friction welding comprising a rotatable shaft which is biased toward a workpiece to plasticize an engaged area of the workpiece. A sleeve element moves toward the workpiece as the shaft is removed in order to push plasticized material back into the workpiece.
U.S. Patent Application Publication No. US 2002/0014516 shows a friction stir welding tool comprising a probe including a shank, shoulder and a pin disposed through the shoulder and into the shank, wherein the pin and the shoulder at least include a coating comprised of a super abrasive material, and having a collar around a portion of the shoulder and the shank to thereby prevent movement of the shoulder relative to the shank, and incorporating thermal management by providing a thermal flow barrier between the shoulder and the shank, and between the collar and the tool.
U.S. Patent Application Publication No. US 2001/0004989 shows a friction stir welding tool having a cylindrical body and at least one flash cutter formed integrally to the cylindrical body of the tool.
Other patents and applications showing FSW technology include U.S. Pat. No. 6,543,670 showing an interface preparation for weld joints, U.S. Patent Application Publication No. US 2001/0040179 showing a friction agitation joining apparatus for joining a plurality of abutted members, U.S. Pat. No. 5,875,953 showing a method and apparatus for effecting interference fit of two parts by accelerating the part or parts, U.S. Pat. No. 5,460,317 showing friction welding utilizing a number of differently shaped pin-tools, U.S. Pat. No. 6,367,681 showing a friction stir welding apparatus and method with a fairly typical stir welding tool, U.S. Pat. No. 6,516,992 showing one embodiment having a threaded pin-tool, U.S. Pat. No. 6,230,957 showing a method of using friction stir welding to repair weld defects and to help avoid weld defects in intersecting welds, U.S. Pat. No. 206,268 showing a friction stir welding pin-tool with internal flow channels, U.S. Pat. No. 5,971,251 showing a method of welding a terminal to a flat flexible cable, U.S. Pat. No. 6,325,273 showing a friction welding apparatus and method showing one or more metal with a spaced apart probes having a crescent shaped cross-section, U.S. Pat. No. 6,299,048 showing a pin-tool having threaded exterior surfaces, U.S. Pat. No. 6,264,088 showing pin-tools having a threaded exterior surface, U.S. Pat. No. 6,227,430 showing a friction stir weld tool for thick weld joints having four sections of thread tapers, U.S. Pat. No. 6,053,391 showing a friction stir welding tool having a unique thread configuration, U.S. Pat. No. 6,029,879 showing a probe having both right-handed and left-handed threads, U.S. Pat. No. 5,893,507 showing an auto-adjustable pin-tool for friction stir welding with what appears to be a traditional pin-tool, U.S. Pat. No. 5,713,507 showing a programmable friction stir welding process with a pin depth sensor, U.S. Pat. No. 6,138,895 showing a manual adjustable probe tool for friction stir welding, U.S. Pat. No. 6,302,315 showing a friction stir welding machine and method having a threaded pin-tool shown in FIG. 5, U.S. Pat. No. 3,822,821 showing a friction welding apparatus which includes a carrier member to receive a component to be friction welded to the workpiece, U.S. Pat. No. 5,718,366 showing a friction stir welding tool for welding variable thickness workpieces, U.S. Pat. No. 6,050,475 showing a method and apparatus for controlling downforce during friction stir welding, and finally, U.S. Pat. No. 5,697,544 showing an adjustable pin-tool for friction stir welding.
Foreign patents have also been filed for friction stir weld improvements. FIG. 2D of Great Britain Patent No. GB 2 306 366 shows a probe having a plurality of projections for mixing plasticized material. European Patent Application No. EP 0 810 055 as well as PCT Patent Application WO 02/070186 also show friction stir welding pin-tool.
While many improvements have been initiated, none are believed to satisfactorily address pin-tool strength, durability, wear resistance and stress management.